Moving ElectricityMoving ElectricityIf charges in a conductor (like a If charges in a conductor (like a

metal) are connected to a battery metal) are connected to a battery or source of electric potential or source of electric potential

difference, they will move.difference, they will move.

Electric CurrentElectric Current

Current is the movement or flow of Current is the movement or flow of charges.charges.

Current = I = charges/time = Current = I = charges/time = coulombs/sec = ampscoulombs/sec = amps

1 Amp of current is a lot of current 1 Amp of current is a lot of current (relatively speaking)(relatively speaking)

Electric Current & PeopleElectric Current & People

Range of current and its affects on humansRange of current and its affects on humans 1 mA (.001A) Slight tingling1 mA (.001A) Slight tingling 5 mA (.005A) Slight shock, disturbing5 mA (.005A) Slight shock, disturbing 6-30 mA painful shock, muscle control lost6-30 mA painful shock, muscle control lost 50-150 mA Extreme pain, resp. arrest. Death 50-150 mA Extreme pain, resp. arrest. Death

possiblepossible 1000-4300 mA Death likely, rhythmic pumping of 1000-4300 mA Death likely, rhythmic pumping of

heart ceasesheart ceases The good thing is our bodies have a lot of The good thing is our bodies have a lot of

resistance (100,000 ohms – ish) so we have lots of resistance (100,000 ohms – ish) so we have lots of resistance to current flow (but, our resistance goes resistance to current flow (but, our resistance goes down if we’re wet or wearing copper clothing)down if we’re wet or wearing copper clothing)

Ohm’s Law: resistance & resistorsOhm’s Law: resistance & resistors

To produce a current a “difference in To produce a current a “difference in potential” is required (voltage) . potential” is required (voltage) .

The Current (I) which flows in a The Current (I) which flows in a conductor is proportional to this conductor is proportional to this Voltage (V).Voltage (V).

The Resistance of the circuit also The Resistance of the circuit also influences the flow of charge.influences the flow of charge.

Ohm’s Law: V = I ROhm’s Law: V = I R R = resistance = ohms R = resistance = ohms ΩΩ

ResistorsResistors

Resistors resist the flow of current.Resistors resist the flow of current. Resistors are used in circuits to control Resistors are used in circuits to control

or regulate the amount of currentor regulate the amount of current Many simple electrical devices are Many simple electrical devices are

simple resistors, examples include hot simple resistors, examples include hot glue guns, waffle irons, clothes irons, glue guns, waffle irons, clothes irons, toasters.toasters.

In these examples resistors heat up as In these examples resistors heat up as they absorb energy provided by the they absorb energy provided by the moving charges.moving charges.

ResistivityResistivity

The resistance of a material depends The resistance of a material depends on its geometry and the type of on its geometry and the type of material its made of.material its made of.

Resistivity is a property of a material Resistivity is a property of a material which tells you how much it resists which tells you how much it resists current flow. The symbol is current flow. The symbol is ρρ..

R (resistance) = R (resistance) = ρρL/A where L = L/A where L = length of the conductor and A is the length of the conductor and A is the cross-sectional area.cross-sectional area.

ResistivityResistivity

MaterialMaterial ResistivityResistivity

CopperCopper 1.68 x 101.68 x 10-8-8

GoldGold 2.44 x 102.44 x 10-8-8

IronIron 9.71 x 109.71 x 10-8-8

WaffleWaffle 812 x 10812 x 1088

Electric PowerElectric Power

Watt?, not another electricity topicWatt?, not another electricity topic Electric Power = energy used per Electric Power = energy used per

timetime P = J/sec = ? (yes)P = J/sec = ? (yes) For electricity, P = VI = IFor electricity, P = VI = I22R = VR = V22/R/R Many electrical devices are rated by Many electrical devices are rated by

their power usage. For example, a their power usage. For example, a 100W bulb uses 100 joules/sec.100W bulb uses 100 joules/sec.